1. Technical Field
The present invention relates to a driving apparatus.
2. Related Art
With reference to an image reading apparatus that includes a scanner unit for reading a source document, a stepping motor that moves the scanner unit, and an ADF including an ADF motor that transports the source document, a technique is known that controls the excitation phase of the stepping motor to utilize the driving force of the stepping motor to fix the scanner unit at an ADF reading position, so as to read the source document transported by the ADF to the ADF reading position through the scanner unit, for example as disclosed in JP-A-2001-268316. According to this document, the scanner unit is prevented from being displaced by the vibration of the ADF motor while reading the source document. In this driving apparatus, the stepping motor is driven by a first motor driver and a second motor driver that supply a current to an A-phase winding and a B-phase winding, respectively, in accordance with a signal from a CPU or a gate array.
In addition, for example JP-A-9-163798 discloses a driving apparatus that includes a two-phase stepping motor, a driver that drives the stepping motor, two D/A converters that convert an input signal and output the converted signal, and a microcomputer that outputs a signal to the D/A converters and the driver. In this driving apparatus, an excitation signal from the microcomputer is inputted to the driver through the respective D/A converters, and the driver drives the two-phase stepping motor with a constant current.
A driving apparatus used for image processing requires the same number of D/A converters that convert a digital signal from the CPU and the microcomputer into an analog signal as the number of motors. For example, in the case where the ADF motor is a single-phase motor and the stepping motor is a two-phase motor, three D/A converters are necessary. However, since the driving apparatus is normally incorporated in an image reading apparatus or the like, it is desirable to simplify the structure of the driving apparatus, to reduce the space occupied by the driving apparatus.